The field of the invention relates generally to electric motors, and more specifically, to methods and systems for operating electric motors.
Typical electric motor systems include a motor controller and an electric motor. The motor controller receives power from an alternating current (AC) power supply, and applies it to a rectifier and to capacitors to generate a smoothed direct current (DC) voltage. The motor controller then supplies a chopped DC voltage to the electric motor through an inverter, which uses the power to drive a load.
Capacitors typically used in motor controllers include electrolytic capacitors with high capacitances (about several hundreds μF). The high capacitances cause the capacitors of the motor controller to be bulky and expensive. These capacitors necessitate a larger motor controller and may reduce the lifespan of the motor controller. New drive technologies target having substantially reduced capacitance capacitors to reduce the size and expense of the electrolytic capacitors. As the energy storage elements (capacitors) have been reduced in the motor drives, the motor phase current may not reach typical steady state waveforms and torque production has a ripple component that varies in amplitude as a function of the motor load point and the input voltage to the system. Typical control algorithms regulating steady state motor currents cannot deliver constant average torque performance. As the torque production is varying as a function of the input source frequency, the motor speed is constantly varying.